1. Field of the Invention
The invention relates to a liquid filling apparatus and more particularly to an improvement in an apparatus that fills containers with liquid and is provided with liquid flow meters.
2. Prior Art
Liquid filling apparatuses that fill containers with liquid have been known, and one type thereof is a flow meter type liquid filling apparatus.
A typical flow type liquid filling apparatus includes a plurality of filling nozzles that have feed-out openings and opening-and-closing valves, valve actuating means which are installed at positions that correspond to the respective filling nozzles and which open and close the valves of the respective filling nozzles, a reservoir tank which stores a liquid, a liquid supplying means which is connected to the upstream side of the reservoir tank, an air pressure adjustment means which adjusts the air pressure inside the reservoir tank, liquid pipe channels which branch from the reservoir tank via a distribution chamber and is connected to the respective filling nozzles, and flow meters which are disposed in the branched liquid pipe channel so as to correspond to the respective filling nozzles.
Japanese Patent Application Laid-Open (Kokai) No. 11-193094 discloses a rotary type liquid filling apparatus.
This filling apparatus includes filling mechanisms which are disposed at fixed intervals in the circumferential direction on a rotating body that rotates continuously and fill containers with a liquid. The apparatus further includes a reservoir tank which stores the liquid, a liquid supplying means connected to the reservoir tank, a pressurizing means which pressurizes the interior of the reservoir tank, and liquid pipe channels which branch from the reservoir tank via a distribution chamber and are connected to the respective filling nozzles.
In this liquid filling apparatus, the pressure-adjustment valve of the pressurizing means is controlled on the basis of detection signals of a liquid pressure sensor that is installed adjacent to the reservoir tank so that air at a constant pressure is introduced into the reservoir tank. When it is detected by a liquid surface sensor that the liquid surface level inside the reservoir tank has dropped below a specified height, the liquid supplying means is actuated on the basis of the detection signal of this liquid surface level sensor so as to replenish the liquid inside the reservoir tank, thus maintaining the liquid pressure inside the reservoir tank and liquid pipe channels at a constant value.
Such liquid filling apparatuses include an apparatus in which flow meters corresponding to the respective filling nozzles are disposed in the branched liquid pipe channel. In this filling apparatus, the filling valves are opened as a result of the actuation of a valve actuating means at a specified timing by a control device at the time of filling, and the filling valves are closed as a result of the actuation of the valve actuating means by the control device at a point in time where the flow rate detected by the flow meters has reached a specified value, so that the amount of liquid with which the containers (e.g., bags) are filled is maintained at a constant value.
In cases where the liquid is flowing through the pipe channels at a certain flow velocity or greater, i.e., in cases where the valves are in a fully open state, the flow rate in the liquid pipe channels measured by such flow meters can be accurately measured even if the liquid pressure is not constant. However, when the valves open or close, it is difficult to achieve an accurate measurement of the flow rate (injection amount) of the liquid flowing through the pipe channels, since the flow velocity is small and varies abruptly. Furthermore, this flow rate fluctuates greatly with the liquid pressure. Accordingly, in a flow meter type liquid filling apparatus, it is necessary to maintain the liquid pressure in the vicinity of the filling nozzles at a constant value in order to maintain the amount of liquid with which the containers are filled (including the injection amount) at a constant value.
However, conventional flow meter type liquid filling apparatuses have problems as follows:
(1) Since the precision of the control of the air pressure in the reservoir tank by the pressurizing means is not very good (i.e., the air pressure inside the reservoir tank shows large fluctuations), it is difficult to maintain the liquid pressure at a constant value. Especially in the case of liquids that have a low viscosity, the liquid pressure used for filling must be set at a low value, so that the air pressure inside the reservoir tank must also be controlled to a low value. In such cases, however, control with good precision is achieved in a conventional apparatus.
(2) Even if the liquid pressure in the reservoir tank or in the liquid pipe channel adjacent to the reservoir tank is maintained at a constant value, the liquid pressure in the vicinity of the filling nozzles may not be constant. More specifically, the pressure loss caused by the resistance of the piping extending from the installation position of the liquid pressure sensor (i.e., the liquid pressure measurement position) to the filling nozzles increases with an increase in the viscosity of the liquid; and if the temperature of the liquid varies or the air temperature varies (e.g., between morning and noontime) so that the viscosity of the liquid varies, then the liquid pressure in the vicinity of the filling nozzles will fluctuate even in cases where the liquid pressure sensor shows the same liquid pressure.
(3) There are also problems in the detection precision itself of the liquid pressure detected by the liquid pressure sensor. In other words, in cases where the valves of a plurality of filling nozzles are successively opened and closed, an abnormal pressure is outputted as a result of the phenomenon of water hammer when the valves are closed. Furthermore, air contained in the liquid may remain in the position of the liquid pressure sensor, so that sharp accurate detection becomes impossible because of the compressibility of air.
Accordingly, the object of the present invention is to eliminate such problems in a conventional flow meter type liquid filling apparatus, so that the liquid pressure in the vicinity of the filling nozzles is maintained at a constant value, and the amount of liquid with which the containers are filled is maintained at a constant value.
The above object is accomplished by a unique structure for a flow meter type liquid filling apparatus that comprises:
a plurality of filling nozzles each having a feed-out opening and a valve that opens and closes,
a valve actuating means installed at a position that corresponds to each filling nozzle and opens and closes the valve of each filling nozzle,
a reservoir tank which stores a liquid therein,
a liquid supplying means connected to an upstream side of the reservoir tank,
an air pressure adjustment means which adjusts air pressure inside the reservoir tank,
a liquid pipe extending from the reservoir tank to a distribution chamber and then branched into liquid pipe channels each connected to each one of the filling nozzles,
a liquid pressure sensor which detects a pressure of a liquid inside the liquid pipe, and
a flow meter disposed on each one of the liquid pipe channels at a position that corresponds to each filling nozzle; wherein
the air pressure adjustment means is actuated on the basis of a detection signal of the liquid pressure sensor, thus adjusting the air pressure inside the reservoir tank so that the pressure of the liquid inside the liquid pipe is maintained at a constant value, and
the valve of each one of the filling nozzles is opened by the valve actuating means at a specified timing and is closed by the valve actuating means on the basis of the measurement signal of each one of the flow meters, thus filling containers with a fixed amount of a filling liquid; and wherein
the air pressure adjustment means is comprised of:
a pressurized air supply source,
an air supply amount control valve which is provided between the pressurized air supply source and the reservoir tank and controls the amount of pressurized air that is supplied to the reservoir tank, and
an air discharge amount control valve which is connected to the reservoir tank and controls the amount of pressurized air that is discharged from the interior of the reservoir tank.
In this liquid filling apparatus, when the liquid pressure detected by the liquid pressure sensor is smaller than a set value (target value), the air supply amount control valve is opened; and when such a detected liquid pressure is larger than the set value (target value), then the air discharge amount control valve is opened. In the conventional apparatus, the air pressure inside the reservoir tank is controlled by a single control valve that is used for air supply. Accordingly, the amount of fluctuation in the air pressure is generally large, and a correction is unable in the case of overshooting. In the present invention, however, the air pressure inside the tank is precisely controlled by two control valves, i.e., one for air supply and one for air discharge. Thus, the liquid pressure inside the liquid pipe channel can be precisely controlled to a set value (target value). This is especially advantageous in the case of a low-viscosity liquid for which a lower air pressure is employed (in order to set the liquid pressure at a low value).
In order to accomplish a more precise control, it is desirable that the air supply amount control valve and air discharge amount control valve be proportional-control valves. A proportional-control valve is a valve in which its degree of opening is controlled in proportion to the inputted voltage. Such a valve can be controlled to an appropriate degree of opening so as to correspond to the magnitude of the detected value of the liquid pressure. In other word, the proportional-control valve is controlled to a degree of opening that is proportional to the dissociation width between, for instance, the detected value of the liquid pressure detected by the liquid pressure sensor and the set value (target value). As a result, when the dissociation width is small, the degree of opening is small, so that the fluctuation in the air pressure (and liquid pressure) is slight, and fine control is performed. On the other hand, when the dissociation width is large, then the degree of opening is large so that the liquid pressure quickly approaches the set value. In any event, with the use of proportional-control valves, the fluctuation width can be reduced, and a precise control is performed.
Another type of air pressure adjustment means of the present invention that makes a precise control on the air inside the reservoir tank is comprised of:
a pressurized air supply source,
a plurality of air supply path provided in parallel between the pressurized air supply source and the reservoir tank,
air supply path opening-and-closing valves that open and close the air supply paths
a plurality of air discharge paths connected in parallel to the reservoir tank,
air discharge path opening-and-closing valves that open and close the air discharge paths, and
a control device that controls, based upon a detection signal of the liquid pressure sensor, an opening and closing operations of the air supply path opening-and-closing valves and discharge path opening-and-closing valves.
It is preferable that the air supply path opening-and-closing valves and the air discharge path opening-and-closing valves are electromagnetic valves. A setting as to which air supply path opening-and-closing valve and which air discharge path opening-and-closing valve is selected (so as to be opened) in response to the detection signal of the liquid pressure sensor is made in the control device. Based upon such a setting, the control device selects a particular air supply path opening-and-closing valve and air discharge path opening-and-closing valve that correspond to the detection signal of the liquid pressure sensor, thus opening the corresponding air supply path opening-and-closing valve and air discharge path opening-and-closing valve.
For instance, by way of providing throttle valves on the respective air supply path and air discharge path, the amount of air flow inside the air supply path and air discharge path is set by the throttle valve to be different from each other. When the dissociation width of the detected value of the liquid pressure sensor and the set value (target value) is large, the air supply path or the air discharge path that allow a larger flow amount is selected (in other word, the corresponding air supply path opening-and-closing valve or air discharge path opening-and-closing valve is opened). As a result, as in the case of the proportional-control valves, when the dissociation width is small, changes in the air pressure (and liquid pressure) is moderate, and a fine control is performed. On the other hand, when the dissociation width is large, then the liquid pressure becomes closer to the set value (target value). Thus, in either case, the changes in amount of fluctuation of the liquid pressure can be small, and a precise control is performed.
It is also possible to make such a setting that a plurality of air supply paths and air discharge paths are selected depending on necessity.
Furthermore, the flow meter type liquid filling apparatus of the present invention can be applied to a rotary type apparatus as seen in prior art. In this case, for example, the filling nozzles are disposed at fixed intervals in a plurality of locations in the circumferential direction on a rotating body which is attached to a hollow rotary shaft connected to a driving means and which rotates continuously, the flow meters and valve actuating means are rotated together with the filling nozzles, and a rotary joint is disposed in coaxial with the hollow rotary shaft so that the rotary joint forms a part of the liquid pipe channel, and the distribution chamber is formed on the rotatable lower section of this rotary joint.
The above object of the present invention is further accomplished by a still another unique structure for a flow meter type liquid filling apparatus that comprises:
a plurality of filling nozzles each having a feed-out opening and a valve that opens and closes,
a valve actuating means installed at a position that corresponds to each filling nozzle and opens and closes the valve of each filling nozzle,
a reservoir tank which stores a liquid therein,
a liquid supplying means connected to an upstream side of the reservoir tank,
an air pressure adjustment means which adjusts air pressure inside the reservoir tank,
a liquid pipe extending from the reservoir tank to a distribution chamber and then branched into liquid pipe channels each connected to each one of the filling nozzles,
a liquid pressure sensor which detects a pressure of a liquid inside the liquid pipe, and
a flow meter disposed on each one of the liquid pipe channels at a position that corresponds to each filling nozzle; wherein
the air pressure adjustment means is actuated on the basis of a detection signal of the liquid pressure sensor, thus adjusting the air pressure inside the reservoir tank so that the pressure of the liquid inside the liquid pipe is maintained at a constant value, and
the valve of each one of the filling nozzles is opened by the valve actuating means at a specified timing and is closed by the valve actuating means on the basis of a measurement signal of each one of the flow meters, thus filling containers with a fixed amount of a filling liquid; and wherein
the liquid pressure sensor is disposed on a distribution chamber or on a vertical portion that is a part of the liquid pipe and directly above the distribution chamber.
A plurality of liquid pipe channels branch toward the filling nozzles from the distribution chamber; accordingly, the distribution chamber is formed so as to have a larger cross-sectional area than the liquid pipe channel up to this point. As a result, there is a stagnation of the liquid flow in the distribution chamber, so that the flow velocity of the liquid is reduced, and the phenomenon of water hammer is alleviated here. Thus, an accurate detection is performed by the liquid pressure sensor. Furthermore, of the various locations in the liquid pipe channel where the liquid pressure sensor can be installed, the distribution chamber is positionally the closest to the filling nozzles; accordingly, the pressure loss caused by the piping resistance is correspondingly low, and the liquid pressure in the vicinity of the filling nozzles tends to be less affected by variations in the viscosity of the liquid.
Meanwhile, the accumulation of air in the vertical portion of the liquid pipe channel directly above the distribution chamber is prevented, and an accurate detection is performed by the liquid pressure sensor. Furthermore, since the liquid pressure sensor is disposed near the filling nozzles, this arrangement is advantageous in that the liquid pressure in the vicinity of the filling nozzles tends not to be affected by variations in the viscosity of the liquid.
Furthermore, the above-described flow meter type liquid filling apparatus of the present invention can also be suitably applied to a rotary type apparatus as seen in the prior art. In this case, for example, the filling nozzles are disposed at fixed intervals in a plurality of locations in the circumferential direction on a rotating body which is attached to a hollow rotary shaft connected to a driving means and which rotates continuously, the flow meters and valve actuating means are rotated together with the filling nozzles, and a rotary joint is disposed in coaxial with the hollow rotary shaft so that the rotary joint forms a part of the liquid pipe channel, and the distribution chamber is formed on the rotatable lower section of this rotary joint, while the liquid pipe channel is vertically connected to the fixed upper section of the rotary joint. When the liquid pressure sensor is disposed on the distribution chamber, the liquid pressure sensor is rotated together with the distribution chamber. However, when the liquid pressure sensor is disposed in the vertical portion of the liquid pipe channel, the liquid pressure sensor is not rotated.
In the flow meter type liquid filling apparatuses described above, it is desirable that a liquid surface level detection means which detects the liquid surface level inside the reservoir tank be provided. The liquid surface level detection means controls, by way of detection signals thereof, the liquid supplying means, thus maintaining the liquid surface level at a constant value. By maintaining the liquid surface level at a constant value, the volume of the head space (that is a space in which air is present) inside the reservoir tank is maintained at a constant value. As a result, the operation of the air pressure adjustment means in the head space can be maintained constantly, and a more stable control of the liquid pressure is performed. The reason for this is that since air is compressible, a large fluctuation in the volume of the head space is accompanied by a fluctuation in the effect of the same amount of air supply or discharge on the air pressure in the head space but this fluctuation can be suppressed.
Furthermore, in the above structure, the above-described liquid supply means is, in concrete terms, comprised of a pump, which is connected to the liquid supply source, and a liquid supply amount control valve, which is interposed between this pump and the reservoir tank; and the liquid supply amount control valve is controlled on the basis of the detection signal of the liquid surface level detection means. A proportional-control valve could be used as the liquid supply amount control valve. The function of the proportional-control valve is described above. Thus, the valve is controlled to an appropriate degree of opening corresponding to the magnitude of the detected value of the liquid surface level by, for instance, setting the degree of opening at a degree that is proportional to the dissociation width between the detected value and set value (target value) of the liquid surface level. As a result, the fluctuation width of the liquid surface level can be reduced, and a precise control is performed.
In the above structure, furthermore, it is desirable that the liquid pressure sensor be disposed between the above-described pump and the liquid supply amount control valve, thus controlling the number of revolution of the pump based upon the detection signal of the liquid pressure sensor. In concrete terms, the number of revolution of the pump is lowered when the liquid pressure sensor detects a high pressure, so that the pressure load on the pump and liquid is alleviated or eliminated. If the number of revolution of the pump is not lowered under a high pressure, the liquid is subjected to kneading by strong pressure load inside the pump, causing the liquid in the pump to have a volume increase and a change in composition.